DESCRIPTION: (Applicant's Abstract) The cannabinoid receptor, in addition to being the initial site of action for the abuse drug marijuana, serves important physiological roles in pain perception and motor coordination. The overall goal of this project is to understand the molecular mechanisms of regulation of the neuronal cannabinoid receptor (CB1). It has been well established that tolerance develops to the effects of cannabinoids. We have evidence that alterations in levels of the cannabinoid receptor occur during tolerance. Therefore, specific aim 1 will examine the regulation of the cannabinoid receptor during chronic exposure to cannabinoids in transfected cells. This aim will address post-transcriptional regulation of the CB1 receptor by utilizing CH0 cells transfected with CB1 receptor cDNA. These cell lines facilitate the study of drug effects on receptor levels, receptor localization and alterations in signal transduction. The studies proposed in specific aim 2 address transcriptional and post-transcriptional regulation of the endogenous cannabinoid receptor. These studies are conducted in neuronal cell lines and primary culture in which receptors are not overexpressed, and although CB1 receptor binding cannot be easily assessed, change in CB1 gene expression can be studied. Cerebellar neurons in primary culture will be studied since they can form synapses and thus mimic normal neuronal relationships. Specific aim 3 will address the regulation of the CB1 receptor gene in an in vivo system. These studies will complement in specific aim 4 which is to characterize the gene for the mouse brain cannabinoid receptor and identify elements in the gene which may be responsible for regulation of receptor expression. Although the mouse is one of the primary animal models for the study of cannabinoids, the sequence of the gene encoding this receptor has not been elucidated. We have cloned the mouse brain cannabinoid receptor gene from a genomic library, and will characterize the 5' and 3' regions of this gene to determine regulatory regions. Understanding the molecular mechanisms underlying the regulation of the neuronal cannabinoid receptor will contribute significantly to our knowledge of this receptor at which marijuana and the endogenous cannabinoids act. This, in turn, may lead to a better understanding of marijuana abuse in humans.